Various apparatus are used in the drive and control mechanisms for the rotors of aircraft, including helicopter type aircraft, for varying the pitch or angle of attack of the blades of a propeller to control lift or to control horizontal flight. Conventionally, the blades are controlled so that all blades change pitch simultaneously to assume various angles corresponding to the control desired. Controlling and varying the propeller pitch most often is accomplished through a gear train including differential gear means. The gear train normally drives the main rotor for the propeller, and variable gear means are drivingly coupled to the propeller blades for varying the pitch thereof. Heretofore, such gear trains often have employed one or more planetary gearsets employing various auxiliary gears for varying the blade pitch. Such apparatus have been cumbersome and require an exorbitant amount of space.
For instance, in U.S. Pat. Nos. 1,596,511 and 1,986,229 to Pistolesi and Stanley, dated Aug. 17, 1926 and Jan. 1, 1935, respectively, the variable input is through the outside ring gears of a planetary gearset arrangement, including auxiliary gear means disposed completely outside the bounds of the planetary gear arrangement.
In other such systems for controlling or varying propeller pitch, the variable drive input is to the planetary gears or planetary gear carriers of the gearsets, again requiring cumbersome mechanics for coupling the gearsets and the drive train outside the bounds of the planetary gearsets. Examples of such systems are shown in U.S. Pat. Nos. 2,020,366 and 2,491,260 to MacCallum and Green, dated Nov. 12, 1935 and Dec. 13, 1949, respectively.
This invention is directed to solving the above problems by an unusual arrangement of gearing that allows the differential speed variations to take place in a much more compact space with less number of gears by stacking two planetary gearsets in juxtaposition, with no additional differential gearset other than the main, required output gearset.